This application is based upon and claims priority to German Patent Application 199 43 653.3 filed Sep. 13, 1999, and German Patent Application 100 36 203.6 filed Jul. 24, 2000, which applications are herein expressly incorporated by reference.
The invention relates to a cross member unit for connecting two joint yokes of a universal joint. The cross member unit includes a cross member with four arms. Two arms are arranged on each common axis. A bearing bush is provided on each arm. Also, rolling contact members rotatably support the bearing bushes on the arms.
DE 44 39 998 A1 illustrates a cross member unit with a cross member having four arms. Each arm has a bearing bush rotatably supported on the arm by rolling contact members. A spring element is provided per arm. The spring element is supported between the inner base face of the bearing bush and the arm. The contact face of the spring element is spherical. Thus, the contact with the inner base face is point-like. The spring element is manufactured from high-tensile plastics. The purpose of using the spring element is to compensate for an assembly-related tolerance. At the same time, the spring permits the arm to escape elastically in the bearing bush.
DE 197 18 896 A1 discloses a universal joint having a first joint yoke, a second joint yoke and a cross member. Pairs of arms are arranged on the two axes positioned perpendicularly relative to one another. The joint yokes are pivotably supported on the axes via bearings mounted in the bearing eyes of the joint yokes. The bearings have bearing bushes and rolling contact members. The bearings and the cross member form the unit commonly referred to as cross member unit.
In the case of heavy driveshafts with diameters in excess of 200 mm, the balancing qualities commonly required today can only be guaranteed for speeds up to 2000 rpm.
It is the object of the present invention to provide a cross member unit which ensures improved centering in connection with the joint yokes at higher speeds.
In accordance with the invention, a cross member unit to connect two joint yokes of a universal joint includes a cross member with four arms. Two arms each form a pair. Each pair of arms is centered on a common axis. Each arm includes a cylindrical outer face and an end face. Each arm has a bore centered on the respective axis. The bore starts from the end face. The two axes extend perpendicularly relative to one another. A bearing bush is on each arm. The bearing bush includes a cylindrical casing and a base which closes the casing at one end. The housing has an inner base face arranged opposite the associated end face of the arm. Rolling contact members rotatably support the bearing bush on the associated arm. A centering element is inserted into the bore on each arm. The centering element includes a spring element and a pressure element. The pressure element has a contact face and a connecting channel to enable passage of a lubricant. The spring element is supported against the arm and loads the pressure element. The contact face of the pressure element projects beyond the end face of the arm and is in contact with the inner base face. The contact face is of a friction bearing material. Due to the pretension generated by the spring elements, the centering elements remain in contact with the inner base faces of the bearing bush even if the joint yokes of a universal-jointed shaft are deformed due to centrifugal forces. As a result, the cross member unit is accurately centered on the axis of rotation of the universal-jointed shaft relative to the joint yoke. The solution in accordance with the invention achieves the required balancing qualities even for speeds up to 4000 revolutions per minute.
In a preferred embodiment, the housing of the centering element is tubular in shape. At one end of the housing, it has a first collar which extends outwardly from the axis of the arm. At the other end of the housing, a second collar extends inwardly towards the axis. The housing is inserted in a centered way into the bore of the arm on the axis. The first collar is supported against the arm. The second collar supports the spring element. An annular gap exists between the circumferential face of the pressure element and the housing. The connecting channel is provided in the form of a first bore. The bore is centered on the axis on the side of the pressure element facing the housing. At least one second bore communicates with the first bore and which, in turn, communicates with the annular gap.
In a preferred embodiment, the contact face of the pressure element is spherical in shape. The contact of the pressure element with the inner base face of the arm is point-like and centered on the axis. As a result of this design measure, a relative movement between the pressure element and the bearing bush is reduced to a minimum.
According to an alternative embodiment, the contact face of the pressure element is planar. The contact between the contact face and the inner base face of the bearing bush is a surface contact. In this way, the axial force between the bearing bush and the pressure element is distributed over a larger surface. Thus, the development of heat and the amount of wear per surface unit is reduced to a minimum.
According to an alternative embodiment, the pressure element includes a cylindrical portion as well as a collar with an annular collar face. Also, a recess with a shoulder is formed in the bore of the arm, in its region adjoining the end face. Further, the outer diameter of the cylindrical portion is adapted to the diameter of the bore. The collar face is supported against the spring element which, in turn, is supported against the shoulder.
The connecting channel of the pressure element is a through-bore centered on the axis. The connecting channel connects the end face with the contact face. The pressure element has at least one groove arranged in the contact face. The groove extends from the through-bore to the circumferential face of the collar. A continuous annular groove is provided in the circumferential face of the cylindrical portion of the pressure element. The continuous annular groove contains a sealing ring that has a sealing effect relative to the bore wall.
The above characteristics allow lubricant to pass through the connecting channel and the grooves into the recess of the bore of the arm. In the case of pressure elements with a planar contact face and surface contact with the inner base face of the bearing bush, it is advantageous that the lubricant reaches the contact zone. As a result, the friction between the two components is reduced to a minimum. Accordingly, the wear of the pressure element is reduced. Consequently, the service life of the parts is increased. Even with high axial pre-tensioning forces and high torques of the driveshaft, the bearing bush remains in its predetermined position relative to the associated arm.
According to a further embodiment, the friction moment which occurs between the contact face and the inner base face, when the bearing bush pivots around the axis relative to the arm, is lower than the friction moment between the pressure element and the spring element as well as between the latter and the arm. This ensured that the pivot movement only occurs between the pressure element and the bearing bush. The pressure element does not rotate relative to the spring element and the arm when the driveshaft is in operation.
According to a further embodiment, the centering element includes an annular disc. The annular disc is supported against the collar face on one side and against the spring element on the other. This disc ensures surface contact between the collar face and the spring element. Without the disc, undesirable settlement symptoms may occur between the spring element and the pressure element. Also, the disc does not rotate relative to the spring element and the arm when the driveshaft is in operation.
Furthermore, the pressure element includes friction bearing material. The friction bearing material, as the base material, includes at least one thermoplastic plastic material and, in the form of admixtures, at least carbon fibers and/or polytetrafluoroethylene (PTFE) and/or carbon. Carbon and PTFE increase the temperature resistance and the wear resistance of the base material. PTFE has good sliding properties. This has a friction-reducing effect on the contact zone between the inner base face and the contact face. The spring element is supported against the housing on one side and against the pressure element on the other. The spring element has a plate spring or a package of plate springs.
The centered bores that extend in the axes of the arms are in the form of through-bores. A lubrication nipple is provided at the point of intersection between the axes. The lubricating nipple connected to the cross member unit provides grease to the rolling contact bearings. The grease is provided through the bores in the four arms which extend in a centered way along the axes and through the bores in the pressure elements. Supplying the rolling contact bearings with grease reduces the amount of wear and increases the service life. A substantial advantage of the described invention is that the centering elements can be inserted subsequently into existing cross member units.
From the following detailed description, taken in conjunction with the drawings and subjoined claims, other objects and advantages of the present invention will become apparent to those skilled in the art.